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Open Roads Forum  >  Towing

 > Tongue Weight Transfer -> TT Axles

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ktmrfs

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Posted: 02/28/12 07:50pm Link  |  Print  |  Notify Moderator

steeleshark wrote:

LarryJM wrote:

steeleshark wrote:

Actually using basic physics, the weight felt on the tongue area does change. If weight is transferred to axles, it is removed from the tongue area. That is why there is a difference in the squat of the vehicle. The weight does not disappear, it just changes locations.


I don't think that is correct since the tongue wts. are actually what the receiver limitations we are talking about here and what it's mounting and design can support and that doesn't change only where the tongue wt. shows up on the various axles.

Larry


If weight is transferred to the axles, where does it come from? The tongue. If you take your rig to a scale and measure with no wd hitch compared to with a wd hitch, you will notice with the hitch a decrease in weight on the rear axle and increase of weight on the TV front axle and the trailer axles. It moves the weight.


this always seems to be a controversial topic. the best way to gain an understanding is to remember weight and force are not the same thing.

Yes, weight is moved, but it moves it from the TV rear axle to the other axles, due to the FORCE applied by the WD hitch bars, it does NOT move or change tongue weight. The weight is transferred to the axles from the upward FORCE applied by the wd bars.

Do this experiment. jump on a scale and weigh yourself. Then push down on the counter next to the scale. Scale reading goes down, but did you magically loose weight? NOPE, now grab the counter and try to lift the counter, scale reading goes up. did you magically gain weight?? NOPE you still weigh the same. The scale reads the sum of the forces applied. the force your body applies to the scale from gavity, and the force applied by your arm against the counter. you applied a counteracting FORCE to the countertop to change the scale reading, but you did not gain or loose weight, you just changed the force applied to the scale. For an object at rest, the sum of the forces must equal zero. same thing with a WD hitch. the spring bars apply an upward force to the tow vehicle rear axle, kinda like lifting up on wheelbarrow handles. The sum of forces must equal zero so that force must be equalized and results in a force applied to the other axles, just like you pulling up on the counter and and this force results in a weight transfer from the rear axle to the other axles. It does nothing to change the tongue weight of the trailer or the tongue weight on the hitch.

* This post was edited 02/28/12 08:27pm by ktmrfs *


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mrnoyb

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Posted: 02/29/12 06:43am Link  |  Print  |  Notify Moderator

Given the tongue/hitch weight does not change, by definition a WD hitch redistributes the weight amongst the available axles. Therefore, does the resulting redistribution of weight increase the available payload of the tow vehicle and decrease the available payload of the travel trailer? If so, by what amount?


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Posted: 02/29/12 07:25am Link  |  Print  |  Notify Moderator

mrnoyb wrote:

Given the tongue/hitch weight does not change, by definition a WD hitch redistributes the weight amongst the available axles. Therefore, does the resulting redistribution of weight increase the available payload of the tow vehicle and decrease the available payload of the travel trailer? If so, by what amount?
If the WDH removes X pounds of load from the TV axles and transfers X pounds of load to the trailer axles,
the amount of other load which can be carried by the TV is increased by X pounds, and
the amount of other load which can be carried by the trailer is decreased by X pounds.

The amount of load transferred to the trailer axles by a properly sized and properly adjusted WDH
will be equal to about 20-30% of the trailer's tongue weight.

Ron

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Posted: 02/29/12 08:52am Link  |  Print  |  Notify Moderator

mkirsch wrote:

Regardless, when figuring weights, you still use the ACTUAL measured dead weight of the trailer tongue.

You can't for example, say "The WD hitch transfers 300lbs to the trailer axles, therefore I can hitch this 1400lb tongue to my 1100lb rated receiver."

The ratings are based on dead weight BEFORE the WD bars are applied.
The actual measured (or estimated) tongue weight is used to select the WDH and bars and to ensure the receiver tongue weight rating is not exceeded.

Only that portion of the tongue weight which actually is carried by the TV needs to be considered when estimating the TV's GVW. When a WDH is used, the trailer-induced load carried by the TV typically is in the range of 70-80% of the tongue weight.

For TV GVWR and GAWR considerations, the weights are based on loads which exist AFTER the WD bars are applied.

Ron

mkirsch

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Posted: 02/29/12 07:54am Link  |  Print  |  Notify Moderator

Regardless, when figuring weights, you still use the ACTUAL measured dead weight of the trailer tongue.

You can't for example, say "The WD hitch transfers 300lbs to the trailer axles, therefore I can hitch this 1400lb tongue to my 1100lb rated receiver."

The ratings are based on dead weight BEFORE the WD bars are applied.


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ewarnerusa

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Posted: 02/29/12 08:11am Link  |  Print  |  Notify Moderator

mkirsch wrote:

Regardless, when figuring weights, you still use the ACTUAL measured dead weight of the trailer tongue.

You can't for example, say "The WD hitch transfers 300lbs to the trailer axles, therefore I can hitch this 1400lb tongue to my 1100lb rated receiver."

The ratings are based on dead weight BEFORE the WD bars are applied.

What about the effect on TV's payload capacity? For example what if there is a situation where the payload + tongue weight before using the WDH has the TV right at its GVWR, and the WDH transfers 300 lbs of the TV's load to the TT axles, then is the GVW of the TV = GVWR - 300lb once applying the WDH? (ignoring the weight of the WDH for simplicity) Seems to me like it would be.

EDIT: On second thought, the TV will still weigh the same after adding the WDH. But the force on the receiver will be reduced by 300 lb. The reactive force required by the rear axle to "hold up" the system will also be reduced by some larger amount, right?

* This post was edited 02/29/12 08:24am by ewarnerusa *


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Posted: 02/29/12 09:11am Link  |  Print  |  Notify Moderator

ewarnerusa wrote:

What about the effect on TV's payload capacity? For example what if there is a situation where the payload + tongue weight before using the WDH has the TV right at its GVWR, and the WDH transfers 300 lbs of the TV's load to the TT axles, then is the GVW of the TV = GVWR - 300lb once applying the WDH? (ignoring the weight of the WDH for simplicity) Seems to me like it would be.

EDIT: On second thought, the TV will still weigh the same after adding the WDH. But the force on the receiver will be reduced by 300 lb. The reactive force required by the rear axle to "hold up" the system will also be reduced by some larger amount, right?
The "weight" of the TV does not change, but the external loads applied to the TV via the receiver do change. The TV's axle loads are determined both by the TV's weight and the external loads.

For example, when a 1000# vertical load is applied to the ball with no WD,
the load on the TV's front axle might be reduced by 500#,
and the load on the TV's rear axle might be increased by 1500#.
The net combined effect on the TV's axles is an addition of 1000#.
So, with no WD applied, the TV's GVW has been increased by 1000#.

When a typical amount of weight distribution is applied,
500# might be added back onto the TV's front axle leaving a net change of 0#,
750# might be removed from the TV's rear axle leaving a net addition of 750#, and
250# might be added to the TT's axles.
With WD applied, the net combined effect on the TV's axles is a addition of 750# (all of which, for this example, would be on the rear axle).
So, with WD applied, the TV's GVW has been increased by 750#.

Ron

mrnoyb

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Posted: 02/29/12 04:44pm Link  |  Print  |  Notify Moderator

The impact to the TV payload capacity with a WD hitch appears to be roughly 75% of the combined TT tongue + WD hitch weight.

In order to obtain an accurate figure would I weigh my TV without the TT hitched and then again with the TT hitched? Would the difference in weights be the amount of TV payload capacity consumed by the TT tongue/hitch weight?

* This post was edited 02/29/12 04:54pm by mrnoyb *

mayorb

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Posted: 02/29/12 01:54pm Link  |  Print  |  Notify Moderator

this thread is why I like rv.net great info

ewarnerusa

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Posted: 02/29/12 11:58am Link  |  Print  |  Notify Moderator

Thanks Ron. That is how I pictured it, but you always hear the worry about tongue weight not changing. It doesn't, the TT didn't get lighter, but its weight got partially distributed back to the TT axles and off of the receiver/tow vehicle.

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